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A 53-year old field trial to evaluate the performance of a range of chemical treatments on eucalypt poles
1989 - IRG/WP 3526
Hardwood pole stubs of Eucalyptus maculata, Eucalyptus pilularis, Eucalyptus saligna and Eucalyptus paniculata were examined for termite attack and fungal decay after 53 years in ground contact. The trial compared eight different chemical treatments with untreated pole stubs of the four species investigated. Untreated Eucalyptus paniculata, a Class I durability species, performed particularly well, whilst treatment of Eucalyptus pilularis with zinc chloride/arsenic mixture afforded the best overall protection of the Class II and Class III durability species.
R S Johnstone, R A Eaton

Charring of Norway spruce wood surface – an alternative surface modification technique?
2019 - IRG/WP 19-40870
Charring is an old wood surface treatment technique, mainly performed on wooden façade elements with the aesthetical aims, but also with the purpose of protection. This flame treatment method can be grouped into heat treatment processes. Below the top charred layer of damaged wood there is a layer which is during flame treatment exposed to high temperatures in anoxic or semi-anoxic conditions. The conditions of forming this layer are similar to those wood is exposed during a conventional thermal modification process to. As such, it might have similar properties than surfaces of conventionally thermally modified wood. Therefore, the aim of our preliminary study was to compare some selected surface characteristics of charred, thermally modified and unmodified Norway spruce wood in order to indicate possible similarities between thermally modified and charred wood surfaces. The charred surfaces that were in the focus of our investigation became substantially darker than surfaces of thermally modified spruce wood, presumably due to substantially higher treatment temperatures. The charred wood became hydrophobic, in wettability similar to that of thermally modified wood. ATR FT-IR measurements indicated that both during charring and thermal modification similar chemical reactions might occurred. The pull-off adhesion strength test of a polyurethane coating that was applied to the substrates exhibited low tensile strength of thermally modified wood and of the charred but undamaged second layer below the surface of flame treated wood. There are only limited scientific data available on properties of charred wood surfaces and so, it is believed that this topic deserves more attention in future, so from scientific as well as from applicative points of view, respectively.
M Petric, M Pavlic, J Zigon

Surface morphology and short-term water uptake of charred and coated wood
2021 - IRG/WP 21-40916
Charring of the wood surface represents a traditional alternative surface treatment technique with the purpose of aesthetics and protection. By the treatment with flame the surface of wood becomes carbonized and a few millimetres thick charred layer is formed on the top of the wooden element. Further, the charred layer can be removed by brushing, which accentuates the structure of the surface. Additionally, for appearance and protective purposes, a different kind of oils and coatings may be applied to the charred wood surfaces. Although this type of wood surface protection has been known for centuries, there is still a lack of knowledge about the water uptake properties of charred and surface finished wood. The aim of the present study was to find out how the treatment with charring, charring and brushing, and surface finishing affect the surface morphology of Norway spruce (S) and European larch (L) wood. By immersing the samples with treated radial surfaces in deionized water, the water uptake in the samples was monitored via the mass increase measurements on the tensiometer. Confocal laser scanning microscope examination showed that charring of wood greatly increased the surface roughness (S by 10-times and L by 6.5-times). Brushing of the charred wood surface further increased surface roughness (S by 21-times and L by for 23-times), completely removing the earlywood structure, while the latewood regions remained present. Surface finishing with water-borne stain noticeably increased only the roughness of the sanded wood surfaces, while the roughness of the other surfaces was not affected. In general, the S wood absorbed more water than the L wood. The highest amount of water was absorbed by the samples with the charred surface (S 0.048 g·cm–2, L 0.031 g·cm–2) and even the surface finishing of these could not prevent water absorption. The water uptake of the other surface types was quite comparable (S about 0.026 g·cm–2, L 0.021 g·cm–2). The higher water uptake seemed to be related to the higher surface roughness or to the specific surface to which the water molecules can attach and possibly penetrate into the wood.
J Zigon

The influence of thermal modification and surface charring to different levels on wettability of Norway spruce wood
2022 - IRG/WP 22-40942
The wood can alternatively be protected from water absorption by thermal modification and charring. Both techniques cause certain chemical and physical changes in the wood, the extent of which depends on the level of temperature applied. The objective of this study was to determine how the combination of charring to different levels and thermal modification affects the chemical, morphological, and wettability properties of the Norway spruce wood. By charring the wood to four different levels, the carbonization began in the earlywood, continued in the latewood, and finally led to the formation of the cracked, in-depth surface char layer. The study of chemical properties showed that both thermal modification and charring of the wood resulted in dehydration of cellulose and hemicelluloses and promoted the presence of chemical units typical of lignin. The roughness of the natural and thermally modified wood surface increased with the increased level of charring. The surface wettability study showed that a higher level of charring gradually decreased the polar part of the surface free energy for both types of wood. Consequently, the contact angle formed between the wood surface and water increased from 70° to 87° for natural spruce wood and from 75° to 101° for thermally modified spruce wood when the degree of charring was increased. These results provide a good basis for further studies on the influence of the level of charring on the properties of wood surfaces, as well as for future research of this technique for protecting wood.
J Žigon, C Gerardin, M E P Wålinder, P Gerardin

A Comparison of Cross-Laminated Timber (CLT) Floor Panels using Finite Element Analysis and Experimental Fire Testing
2022 - IRG/WP 22-40955
Cross-laminated timber (CLT) is a relatively new timber product and has gained popularity in North America and Europe as a construction material. As a sustainable engineered timber product, CLT offers many advantages over solid wood, concrete, or steel construction. However, the use of timber in medium to high rise buildings is often avoided mainly due to its combustible nature. In this paper, a numerical model of a CLT floor panel was developed using the Finite Element (FE) Method in Abaqus. This paper analyses the thermal behaviour of a CLT panel when exposed to a standard test fire. In the modelling of a CLT floor panel, Eurocode 5 temperature-dependent relationships were adopted. The results of the FE model were then compared with the experimental tests performed for a similar-sized panel. The charring rate and temperature distribution across the depth of the CLT panel were investigated for all test specimens and comparisons were made with the experimental results. The comparisons of FE results with experimental results showed that the FE analysis gave reasonably accurate results to allow for the development of full-scale computational models of a prototype CLT building.
M Yasir, A Macilwraith, K Ruane